I am using a 12V battery to run a few circuits that I have. One being my arduino. I bought a three pin, positive 9V/1A regulator and am using it to hook into the power jack on the arduino. After about thirty seconds I notice that the regulator gets extremely hot. I have an Uno w/ Ethernet shield and I am using almost every pin on the board. I'm guessing that the arduino is pulling more than the 1A max rating for the regulator and thats why its getting hot so quick. My question is...Does anyone know how to calculate the total current my Uno would be pulling through the regulator in order to supply all my output pins with current (or have a good formula for it)? Also a 9V/2.2A regulator is the highest output current I could find. Does anyone know of one with higher current rating and where I could get it?
I just read that each I/O pin can put out a max 40mA. So in theory if I have every pin on the board set as an output (which i don't) it would have to pull almost 1 amp of current to supply all my outputs. And even though the regulator says it can run a max of 1A it is probably safe to only run about half that. So that 9V/2.2A regulator should be enough to sustain my setup without burning any components up right?
I bought a three pin, positive 9V/1A regulator and am using it to hook into the power jack on the arduino.
If you're starting with 12V and adding an intermediate regulator, why would you not get a good whatever-voltage-to-5V switching regulator and skip the Arduino regulator?
After about thirty seconds I notice that the regulator gets extremely hot.
What I used for reference...
"This means that for every Watt you dissipate you get 50 degrees C rise. "
(9-5) volts dropped * 0.100 A (estimated) = 0.400 watts = ~20°C rise (68°F). If you start at room temperature (20°C) the regulator will get to 40°C (104°F).
If you really were flowing 1A... (9-5) volts dropped * 1 A = 4 watts = ~200°C rise (392°F) ...the regulator would shutdown.
mattrloper:
My question is...Does anyone know how to calculate the total current my Uno would be pulling through the regulator in order to supply all my output pins with current (or have a good formula for it)?
Try using a multimeter on the input supply...
mattrloper:
I just read that each I/O pin can put out a max 40mA.
Yes, but that doesn't mean it's a good idea.
The datasheet says: "This is a stress rating only and functional operation of the device at these conditions is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability."
And...don't think you can pull 20mA though all pins either. The maximum current allowed through Vcc is 200mA so there's only 200mA available for all your pins (and 200mA is the stress rating - see warning above). You can only light up about 8x20mA LEDs at full brightness.
You're right though, if he's pulling 1 amp through the I/O pins then he's overloading them. There's not enough pins to add up to 1 amp.
I think the 1 Amp thing is only the incorrect conclusion the OP is drawing from the fact that the regulator is getting hot.
Many people think that if a chip is rated at a specific current then that is the current that it can be used at and with no heat sink. The fact is that a current rating is only one parameter and often it is not the limiting one. It is power dissipation that is the limiting factor here. Going from 12V to 5V involves a drop of 7V and therefor if you did draw one amp you would be dissapating 7W, far too much for that surface mount regulator. I have not got the data sheet to hand but I guess it can only handle a watt or so. Therefore even modest currents will make it hot.
The onboard regulator is only good for 800mA - it should shutdown (or blow up) with 1A of current draw.
Its a part like this, maybe a different manufacturer:
Ok that makes sense that its just putting off alot of heat. This thing is a NTE1910. Io - 1A, Pd - 15W.
You might consider directly powering the arduino directly from a UBEC like below. They are more efficient than regulator chips.